As one of audio signals capable of enhancing a realistic feeling of a user, there has been known a binaural signal taking into account transfer characteristics of a sound in the head of the user. A binaural signal indicating a sound from a desired sound source direction is generated by a convolution operation of a head-related transfer function indicating the transfer characteristics of the sound in the head of the user and a monaural audio signal, according to the desired sound source direction, for example.
In order to generate a binaural signal for any sound source direction, it is preferable that head-related transfer functions are prepared beforehand for all sound source directions. However, it is actually not realistic in terms of cost and work effort to measure transfer characteristics of the head of the user for all the sound source directions and then generate head-related transfer functions for all the sound source directions based on the measurement result. Therefore, transfer characteristics of the head of the user are previously measured for some sound source directions, and head-related transfer functions are prepared for those sound source directions. Then, head-related transfer functions for the other sound source directions are obtained by interpolation based on the prepared head-related transfer functions. For example, there has been proposed a technique to obtain transfer characteristics in a desired sound source direction by delaying transfer characteristics by a delay amount in the desired sound source direction, the transfer characteristics being obtained by interpolating transfer characteristics with a delay amount removed therefrom for each of a plurality of sound source directions.
Examples of the related art include Japanese Laid-open Patent Publication No. 2010-41425.